1. Field of the Invention
The present invention generally relates to arrangements for estimating the internal temperature of a vehicle battery.
2. Background Art
Generally, the internal temperature of a battery in a motor vehicle is an important variable to be input for engine charging control. The internal temperature is required to determine an accurate set point for an electronic voltage regulator (EVR) in the battery charging system. A proper set point prevents the battery from being overcharged (and overheating) at temperatures higher than a predetermined threshold and undercharged at temperatures lower than a predetermined threshold.
Generally, known vehicle batteries do not, during normal vehicle operation, incorporate internal temperature sensors due to high cost and difficulty in assuring the sensor is replaced when the battery is replaced in service. One solution is to measure internal battery temperature using a sensor mounted to the outside of the battery casing. The drawback of this method is that temperatures measured using the external sensor do not accurately reflect the battery internal temperature, e.g., the error may be as high as 30° C.
To overcome the accuracy problems in measuring the battery internal temperature with an external sensor, calibration algorithms have been used to compensate for deficiencies. To make the calibration effective, however, the calibration algorithms themselves tend to be complicated because of the interactive thermal dynamic process in the battery and the engine block environment, and without accurate calibration, such measurement algorithms may not prove sufficiently adequate.
Still further, irrespective of whether an internal or external battery temperature sensor is used, it is difficult to achieve both high cost effectiveness and acceptable measurement performance in mass vehicle production.